Although inconclusive, evidence suggests irrigation water and improperly composted livestock manure are possible causes of increased numbers of foodborne illness outbreaks over the past ten years attributed to produce, like baby spinach and iceberg lettuce being contaminated by pathogens such as E. Coli O157:H7 and Salmonella.

Dr. Rick Holley, with the University of Manitoba's Faculty of Agricultural and Food Sciences suggests, although the microorganisms have no effect on livestock, they are being shed after being consumed in feed.

He says there are thermal processes in mills that will kill these pathogens but we fail to control cross contamination.

Dr. Rick Holley-University of Manitoba

After the heating steps that are currently being used, we don't have appropriate controls in place to prevent cross contamination.

That is previously cooked product with dust from areas in plant processing environments where you have raw unprocessed ingredients and so you do have cross contamination taking place.

That's certainly an area where we need to take a serious look at ways of implementing controls and they'll vary depending upon the material being processed.

For example, if you've got a feed mill that's doing a pelleting operation where temperatures normally are used that are sufficient to kill Salmonella and E. Coli, you get a fair amount of dust being generated and it's that dust which we believe to be a carrier that goes back and then contaminates the already cooked pellets.

Dr. Holley says, because the pathogens aren't harmful to the animals and additional measures would add cost, there has been little incentive to take action.

However, he suggests, the best way keep the microorganisms from infecting produce is to keep them out of the cycle.